After the reactive dye is dyed and fixed, although it forms a covalent bond with the fiber, there will always be a small amount of unfixed dye on the fiber, especially in the pores of the fiber. In addition, in the application stage, the dyes in the fiber may also break bonds and continuously form unfixed dyes. In the wet state, these dyes will diffuse out of the fiber, causing color loss and reducing color fastness, especially some dark colors. The product is more obvious. For this reason, in recent years, people have used some fixing agents to treat textiles after dyeing with reactive dyes or after sufficient washing, that is, fixing after dyeing.
Selection of fixing agent
Although the reactive dye and the fiber form a covalent bond by adding alkali to fix the color, the bond will still be hydrolyzed and broken under certain conditions to generate hydrolyzed dye. Removal of inexhaustible hydrolyzed dyes, unbonded dyes, or improper post-soaping treatment conditions will reduce the wet treatment fastness of dyes. Reactive dyes are easily soluble anionic dyes. Try to reduce the solubility of the dye on the fiber, or increase the force between the dye and the fiber, which can improve the washing fastness of the dye and resist the adverse effects of the atmosphere on the dye. In this regard, there are the following common types of fixing agents.
Metal salt fixing agent
It is suitable for reactive dyes that can complex with metal ions, such as dyes with salicylic acid structure. After the dye reacts with the metal ion, insoluble stable complexes can be formed on the fiber, thereby reducing the water solubility of the dye and improving the washing fastness and light fastness of the dyed fabric. Such fixing agents include soluble copper or chromium salts.
Cationic fixing agent
The cationic fixing agent can be combined with the dye anion, the water-soluble group is blocked, and the larger insoluble compound is formed and precipitated on the fiber, thereby improving the washing fastness of the dyed material. Such fixing agents include fixing agent M and fixing agent Y.
Reactive fixing agent
This fixing agent can be divided into two categories. The first type of molecule contains cross-linking groups, which can react with polar groups such as amino and carboxyl groups in dyes and fibers to form covalent bonds. After high-temperature baking, various reactive groups in the resin cross-link and condense. , Form a three-dimensional network protective film on the surface of the fiber, thereby improving the wet processing fastness. The second category is polycations with active groups in the molecule, which can not only chemically react with fibers to form covalent bonds, but also form insoluble salts with dye anions, which can significantly improve the fastness to wet processing, and does not contain formaldehyde.
Fixing agent requirements
(1) Environmental protection, no pollution to the environment;
(2) After the fixing agent is fixed, it should be able to improve all kinds of fastness, including soaping, dry rubbing, wet rubbing and perspiration fastness, etc.;
(3) After being fixed by the fixing agent, the color change should be small, and the shade of the dyed material will not be affected, which is convenient for production control;
(4) The fixing agent must be safe, non-toxic, and not produce toxic or harmful substances during storage and use.